Many cyclic polysiloxanes, including pentamethylcyclopentasiloxane (sometimes referred to hereinafter as D5H) have been commercially available for a number of years. At one time, these materials seemed promising for use in medical applications. They are known to be useful as crosslinkers in silicone coatings and encapsulating materials used in the electronic industry, as well as for other electronic applications, such as composites and adhesives. Hence, synthetic methods therefor are known in the art.
For example, Haines, et al, U.S. Pat. No. 5,395,956, discloses a process for the synthesis of organohydrogensiloxanes, namely cyclic organohyddrogensiloxanes. An hydrozylate intermediate is rearranged via an acidic rearrangement catalyst, such as a sulfonated divinylbenzenestyrene copolymer resin, to form a cyclic organohydrogen-siloxane having the formula
where n=3 to 12. As noted in the patent, such polysiloxanes are known in the art, but this process for its production provides minimal loss of siloxanes due to crosslinking of the siloxanes to high molecular weight byproducts. Accordingly, cyclic polysiloxanes such as pentamethylcyclopentasiloxane are known, but the industry has yet to derive poly(cyclosiloxanes) therefrom.
However, crosslinking different derivatives of cyclic polysiloxanes is known in the art. In particular, Loo, U.S. Pat. No. 5,334,688, discloses a crosslinked polymer or crosslinkable prepolymer, which is the hydrosilation reaction product of a cyclic polysiloxane, an organosilicon compound having at least two Si—H groups, and an optional third ingredient, an aromatic polyene having at least one carbon-carbon double bond. In Loo, U.S. Pat. No. 5,373,077, the divisional of the '688 patent, the aromatic polyene is a required ingredient. These crosslinked polymers, while technically polycyclosiloxanes, are limited to hydrosilation reactions between cyclic polysiloxanes having the formula
wherein R is a saturated, substituted or unsubstituted alkyl or alkoxy group or a substituted or unsubstituted aryl or aryloxy group, R1 is a substituted or unsubstituted hydrocarbon group having at least one nonaromatic carbon-carbon double bond reactive via hydrosilation, and n is 3 or 4; and cyclic polysiloxanes having at least two Si—H groups. However, these compositions are prepared only by way of a hydrosilation reaction wherein a Si—H group reacts with a vinyl or allyl group to provide the Si—O—Si linkages.
Similarly, other multiple component networks (MCNs) have also been prepared. For example, commonly owned U.S. application Ser. No. 09/833,774 discloses multicomponent networks comprising the reaction product of a plurality of multifunctional, allyl-terminated polyethylene glycols linked to a plurality of multifunctional siloxanes having at least two SiH moieties for each siloxane. These multiple component networks (MCNs) as well as the more traditional interpenetrating polymer networks (IPNs) should be distinguished from single component networks or polymerization products that are random aggregates of condensed cyclic siloxanes comprising a great variety of linearly and three dimensionally connected and crosslinked rings. An MCN is defined as a single elastomeric network comprising at least two chemically different covalently-bonded sequences while an IPN consists of two or more unlinked, independent networks
Thus, the need continues to exist for a single component polymer, i.e., a homopolymer, comprising a single polymeric species—namely a particular cyclic polysiloxane, networked in three dimensions to form a poly(cyclosiloxane).